Trap switch constructions in the normally closed protective circuit of burglar alarm systems

ABSTRACT

The trap includes a pliable elongated member which may be a wire, cord or tape having a steel terminal element serving as an armature releasably held by a permanent magnet structure which constitutes one end support holding the elongated member taut. When the armature is detached from the magnet by movement of some part of the protected structure, as for instance a window, a venetian blind or by movement of an intruder, the protective circuit will open, thereby actuating the alarm circuit. The magnet is one terminal of the trap switch. The armature is conductively connected in some manner to the other switch terminal. The pliable elongated member may be a wire offering part of the circuit path while the armature and magnet are engaged. Parts of the protected structure may serve as the pliable member or the armature, as for instance in an example shown, the ladder tapes of a venetian blind serve as the elongated pliable member, while the blind&#39;&#39;s base rail serves as the armature. Both supports for the pliable member may comprise a magnet and armature. In embodiments shown, a single armature is used to shunt two spaced magnets, in which instances, such pair of magnets constitute the switch terminals. The magnet structures preferrably comprise a magnetic block carried in a sheet steel channel having mounting lugs for various placements. The line of direction of the elongated pliable member, is not limited. Force required to dislodge the armature is adjustable.

United States Patent I Lea [151 3,668,582 51 June 6,1972

THE NORMALLY CLOSED PROTECTIVE CIRCUIT 0F BURGLAR ALARM SYSTEMS Lawrence N. Lee, No. 3601 Johnson Ave., Bronx, New York, NY.

221 Filedz on. s, 1970 211 'Appl.No.: 78,128

41 TRAP swrrcn CONSTRUCTIONS 1N 72 Inventor:

[521 US. Cl ..33S/285, ZOO/61.93, 340/276 3,235,302 2/1966 Benson,.lr. ..335/285X Primary Examiner-Bernard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.

Attorney-William T. Haugh and Laforest S. Saulsbury L5 1. Ans m cT The trap includes a pliable elongated member which may be a I wire, cord or tape having a steel terminal element serving as an armature releasably held by a permanent magnet structure which constitutes one end support holding the elongated member taut. When the armature is detached from the magnet by movement of some part of the protected structure, as for instance a window, a venetian blind or by movement of an intruder, the protective circuit will open, thereby actuating the alarm circuit. The magnet is one terminal of the trap switch. The armature is conductively connected in some manner to .the other switch terminal. The pliable elongated member may be a wire offering part of the circuit path while the annature and magnet are engaged. Parts of the protected structure may serve as the pliable member or the armature, as for instance in an example shown, the ladder tapes of a venetian blind serve as the elongated pliable member, while the blind's base rail serves as the armature. Both supports for the pliable member may comprise a magnet and armature. ln embodiments shown, a single armature is used to shunt two spaced magnets, in which instances, such pair of magnets constitute the switch terminals. The magnet structures preferrably comprise a magnetic block carried in a sheet steel Channel having mounting lugs for various placements. The line of direction of the elongated pliable member, is not limited. Force required to :dislodge the armature is adju'stable P'ATiNTEfiJun 6197'2 3, 668,582

sum 2 or 2 FIG. l9 F|G.2O

INVENTOR, Lawence N. Lea,

ATTORNEY- TRAP SWITCH CONSTRUCTKONS IN THE NORMALLY CLOSED PROTECTIVE'CIRCUIT OF BURGLAR ALARM SYSTEMS The present invention relates to electrical switch constructions and more particularly to the type known as traps, for use in normally closed protective circuits of burglar alarm systems; such traps consisting of an elongated pliable member held taut by and between two supports, from at least one of which it is easily releasable. When such member becomes separated from a support, by an unauthorized movement of something in the protected area, the protective circuit would open, thereby actuating the alarm circuit. Said member is called the trap wire.

In prior trap constructions, the release-affording support for the trap wire, utilized a comparatively expensive clamping mechanism to engage a tab terminal on the trap wire. Such support could be mounted in only one relation to the direction of the trap wire, for in use it was mandatory that the trap wire shall be at right angles to the line of clamp jaw movement, and the tab must be along the line of said trap wire. The trap was inoperative otherwise. Other angular relationships between the clamp jaws, tab and wire, were impossible. Many times, mounting surface position in a given installation and its contour, made use of these clamping mounts very impractical and even impossible.

It is therefore an object of this invention to provide novel and improved trap switch constructions which are simple in structure, relatively cheap to manufacture as to tooling and labor costs, and which have a release-affording mount which can be positioned in many ways for proper trap installation and operation, and not limited to the incidents of prior devices, and further, permitting any desired relation as to angular positions between the support means, the trip wire and its terminal lug, and does not require that the terminal lug be in alignment with the trip wire, nor limit the direction of the trip wire in relation to the support therefor.

Another object of this invention is to provide novel and improved trap constructions of the character described, in which parts of the protected structure may serve as part of the switch construction. As will be shown in an embodiment involving a venetian blind, its tapes and base rail serve in the switch structure.

A further object thereof is to provide a novel and improved trap construction of the type set forth, affording adjustment of the force required to separate the trap wire from its release-affording mount. Prior devices never made such provision.

A further object thereof is to provide novel and improved trap construction of the kind described, in which limited movement of the trap wire is permitted without actuating the alarm circuit, as is desirable in installations involving the protection of loosely fitting doors, windows which are subject to V flutter, or involving what the trade calls swingers" as venetian blinds and other things subject to some vibrations.

Still another object of this invention is to provide novel and improved traps of the character set forth, having the-mentioned attributes, which are easy to install in numerous ways for different forms of protection against tampering and intrusion, and which are efficient in carrying out the purposes for which they are designed.

Other objects and advantages will become apparent as this disclosure proceeds.

For the practice of this invention, the essential parts of the trap are an elongated pliable member as a wire, cord or tape held taut between two supports from at least one of which is can be readily pulled free. This release-affording support a permanent. magnet structure whose armature is attached at one end of said pliable elongated member. The trap is associated in various ways with predetermined parts of protected premises structure, so if such parts are moved, and in some instances if the trap wire is cut, or otherwise forced loose of its hold, the protective circuit will be opened, thereby causing the alarm circuit of the burglar alarm system to be actuated.

In embodiments shown, the magnet, its armature and the pliable member are conductive. The wire is releasably associated at both ends with magnetic devices. Parts of the protected structure serve as the pliable member and the armature, in some of the examples of arrangement shown. Another embodiment illustrates a trap in which the wire is along and a bit above the floor of a room, adapted to be tripped by an intruder. Preferred magnet structure comprises a permanent magnet block fitted within a steel channel having mounting lugs in various directions. The magnet is one terminal of the trap switch. The armature is in some manner conductively associated with the second terminal of the trap switch, when the trap is set up to be in operative condition.

In the accompanying drawings forming part of this specification, similar characters of reference indicate corresponding parts in all the views.

FIG. 1 is a perspective view showing a trap switch embodying teachings of this invention. The trap wire is supported taut between two supports which are magnet structures. The ends of said wire have terminal tabs which are the armatures held by attraction by said magnets; said wire being in alignment with said armatures.

FIG. 2 is an elevational view showing the trap of FIG. 1 installed, but the arrangement is such that the trap wire is in right-angle relation with the armatures.

FIG. 3 is a perspective view of the magnet structure employed in the several embodiments of the traps shown herein.

FIG. 4 is a perspective view of a component of the magnet structure.

FIG. 5 is a section taken at line 55 in FIG. 3.

FIG. 6 is a perspective view of an armature.

FIG. 7 is a perspective view of a slightly modified form of the part shown in FIG. 4.

FIG. 8 is a perspective view showing an assembly comprising the magnet structure of FIG. 3, mounted on an insulative base.

FIG. 9 is a rear view of FIG. 8.

FIG. 10 is a section taken at line l0-l0 in FIG. 8.

FIG. 11 is a perspective view differing from FIG. 8, in that it comprises two magnet structures.

FIG. 12 is a bottom view of FIG. 11.

FIG. 13 is an enlarged section taken at line 13l3 in FIG. 1.

FIGS. 14 and 15 are fragmentary views to show the provision to adjust the force required to release the trap wire. These views will also be used to explain how these devices take care of flutter and motion permission to swingers. FIG. 16 is a perspective view of a trap switch similar in construction to that shown in FIG. 1, but of slightly modified construction in a part of the magnet structure.

FIG. 17 is a perspective view of that part in FIG. 16 which is different than what serves for it in the embodiment shown in FIGS. 1, 3 and 7.

FIG. 18 is a section though the magnet structure taken at line 1818 in FIG. 16, but of slightly modified construction.

FIG. 19 is a diagrammatic showing of a trap device of either FIG. 1 or FIG. 16, associated with a venitian blind so any lifting of the blind or swinging of the blind, the trap wire would become separated at one end, thereby causing the alarm to be sounded.

FIG. 20 shows a venetian blind equipped with a trap switch scheme embodying teachings of this invention. Here, the tapes of the blind serve as the trap wire, and the base rail of said blind, serves as the armature.

FIG. 21 shows a trap switch arrangement using the magnetic means shown in FIG. 1 1, associated with a window.

FIG. 22 is a diagrammatic inside view of a window protected by a trap system utilizing teachings of this invention, arranged to set ofi the alarm upon the opening of the window, the cutting of a wire, or should an intruder attempt to enter the premises after breaking the window.

FIG. 23 shows another switch arrangement using this invention, where the trap wire is along the floor of a room and a little above the floor, to be tripped by an intruder, whereby the alarm circuit would be actuated. This view includes a fragmentary showing of the burglar alarm circuit diagram.

In the drawings, the numeral 30 designates generally a pliable conductive wire having at one end, a steel terminal lug 31, which is an armature for engagement by attraction by the permanent magnet structure denoted generally by the numeral 32, preferrably comprising a small block 33 which is a permanent magnet fitted within a sheet steel channel 34, flush as shown in FIG. 13, or slightly recessed as shown at 34 in FIG. 17. The poles of said block are itsfaces, one of which contacts the floor wall of the channel it is in. For said block, a barium ferrite flexible magnet, or the magnet material marketed under the name of Alnico is recommended. Of course, any

permanent magnet structure may be employed for the practice of this invention. In the. specific magnet structure described, the block is provided with a counterbored hole for an assembly screw 35 which is engaged in the threaded hole 36 in the floor wall of the channel piece. To mount the magnet structure 32, the channel piece is preferrably-provided with lugs as shown at 37, 38 or both, and it is very practical that the channel memberbe fashioned as indicated by the numeral 39 in FIG. 17, to provide lugs in angular relation of 90, as 40, 41, and 42', 43, so the magnet structure indicated generally by the numeral 44, can be mounted on differently positioned surfaces. Each mounting lug has a hole therethrough for a screw which may also serve as one of the switch terminals. .Of course, only one of the screws 45, used to mount the magnet structure 44, is used as such terminal. The constructions described,serve on dielectrics as where the installation is on wood. When the protected structure is of metal whereon the magnet structure need be mounted, then an insulative base 46 is provided withsuitable mounting holes 47. The numerals 48, 49 are threaded holes in the base 46, to receive the assembly screws 50, and the binding post screw 51. The embodiment 79' of ,F IG. 1], is akin to 79, but carries two magnet structures indicated as 69 and 69.

To constitute and serve as a switch device, then asin FIG.

23, the trap wire 30 need be normally held taut, between two supports, which I have chosen to be magnetic structures as 44, which act as the switch terminals. Of course, one of these supports may just be a fixed element (not shown)-'offering a binding post to be the second switch terminal. The installation for use, involves associating this trap switch with parts or appurtanences of the premises to be protected, so upon attempted intrusion or other disturbance caused by an unauthorized movement of such parts, the armature-will be pulled off a magnet structure, or should the wire 30 be cut, the protective circuit 54 in which such trap switch is interposed, would open, whereby the alarm circuit 55 of the burglar alarm system set forth-as in the FIG. 23, becomes actuated; such system being illustrated fragmentarily, but is believed fully understood by those versed in the art, so no further illustration or explanation thereof is necessary, and such system may be deemed suitable to include any of the trap switch arrangements herein shown, which will now be described.

In the trap arrangement shown in FIG. 19, the numeral 56 denotes a venetian blind drawn down on its associated window. In alignment, on, or to one side of the opposite window frame parts 57, 57' as shown, there are mounted the permanent magnet structures 44, each holding in attraction an armature 31; said armatures being the terminal lugs or tabs on the conductive trap wire 30 which is held taut between two successive. slats 58, 58, and between the rungs of the ladder tapes 59, 59' which support said slats. For connection of this switch device in circuit, there are the wires 60, 60' leading from-the magnet structures 44. It is evident that upon movement of the blind to cause disassociation of an armature 31 from its related magnet 44, that the protective circuit will be opened, thus activating the alarm circuit. Each end of the trap wire being r'eleasably connected, allows removal of the wire 30 when the premises are in use. Otherwise, if one of the wire ends is permanently anchores to a fixed support (not shown),

it might be objectionable to have the trap wire hanging down, to mar room appearance.

In the trap arrangement shown in FIG. 20, the base rail of the venetian blind, indicated by the numeral 65, is of metal. When the blind 62 is drawn down, the tapes 67 and 67' are taut, and the base rail 65 contacts both magnet structures 44 which are mounted on the window sill. It is evident that upon movement of the blind so that one or both of said magnets are relieved of the base rail 65, that the protective circuit would be opened and the alarm circuit would become activated. The conductors 66, 66' from the magnets respectively, are connected in the protective circuit, to interpose the trap switch. In this embodiment, the base rail 65 serves as the armature for both of the magnets, and the tapes 67, 67' serve as the pliable elongated member, the trap wire, which needs no conductivity to pass current. This trap wire, which here comprises the tapes, is anchored at one end to the head rail 65', and its other end terminates in the armature which is the base rail 65, as mentioned.

In the trap arrangement shown in FIG. 21, the upper member 68 of the window frame, carries the two spaced magnetstructures 69, 69' mounted on a dielectric base 70, which is the unit 79' shown in FIG. 11. Conductors 71, 71 connected to the binding post screws 72, 72' respectively, are the switch connections. in the protective circuit. In similar arrangement as the embodiment shown in FIG. 20, these magnets are bridged by a single armature 31, when the upper sash 73 is closed, at which time the cord 74', which may be nonconductive, is taut; said cord having its other end anchored at 75 to said sash. Should such upper sash be lowered, the armature will become dislodged from the magnets 69, 69 and the protective circuit will become opened, whereupon the alarm circuit will become actuated. Of course, the bottom sash 73 will be associated with a similar trap to effect the shunt to maintain the protective circuit intact while the lower sash is in closing position.

In the trap arrangement-shown in FIG. 22, the conductive trap wires 74, 75 and 76 are spaced close enough that if the window they protect isbroken, even a slim'person could not intrude and enter upon the premises without disturbing at least one of said closely spaced wires so that an armature 31 which is a terminal at the end of each of said wires, shall become pulled ofi the magnet 44 it is associated with, thereby breaking the protective circuit in which said wires 74, 75 and 76 are connected in series. The wires 74 and 76, positioned passed through the eye screws 80, 80, cause alarm actuation upon opening either window sash, as is well known. Cutting any of said wires, would also activate the alarm circuit.

In the trap arrangement shown in FIG. 23, the trap wire 77 held taut a bit above the floor and provided with the terminal tabs 31 serving as armatures for the fixed-to-wall opposite magnets 44, is adapted to be tripped by an intruder into the room 78, thus dislodging at least one of the end terminals of the wire 77 from its associated magnet, causing the protective circuit 54 of the burglar alarm system to be opened, and thereupon, the alarm circuit 55, actuated.

A preferred manner of attachment for the ends of a trap wire to an armature, is shown in FIG. 13, where the engaging loop keeps the wire length intact, and is applicable at all mounting of the trap wires in association with an armature tab.

In prior devices, no provision was made to adjust the force required to pull the trap wire free from the release-affording mount. In the present invention, a change in the amount of overlap of the armature on the magnet, adjusts for the force necessary to accomplish release; such force being substantially proportional to the extent of such overlap. Total overlap, requiring the maximum force to overcome the magnets attraction for its armature, is indicated by the distance a in FIG. 1, and by distance b in FIG. 16. Partial overlap to require a lesser force for armature disassociation, is indicated by the distance 0 in FIG. 13, and by the distance 11" in FIG. 14.

It is to be noted that for total overlap, the channel 39 has its lugs 41, 43 extending from one side wall 52, at each end of the channel, to make the notch 53, so the armature 31 may contact the distal longitudinal edges of the side walls of said channel as shown in FIG. 16.

Also in prior devices, no provision was made to allow for some slight vibration, swing or lost motion" without sounding the alarm. The present invention provides for such movement, keeping the protective circuit intact, because the armature can be shifted somewhat along the magnet it is associated with, and maintain contact, as would occur for instance by slight swing of a Venetian blind, rattle in ill fitting window frames, and other :swingers as they are termed in the trade.

In prior trap devices, a fixed relation of the trap wire with respect to the release-affording mount was mandatory, and such wire had to be in the plane of its terminal tab which engaged such mount. In the present invention the magnet structures may be mounted in any plane, the trap wire could be along any line, and angles x" and y," indicated in the FIGS. 1 and 2 respectively, could be any degree. As one example as shown in FIG. 2, the trap wire 30 is in right-angled relation to the terminal armatures 31 which it carries. Release of the trap wire from its hold, may shift the arrnatures off their magnets, by a sliding or swing movement, or by combined movements of such character.

In prior trap switches, the release-affording mount consisted of a comparatively complicated construction to afford releasable clamping means, which required expensive tools to manufacture and high labor cost to assemble. In the present invention, the making of the magnetic structures involve simple and relatively inexpensive tools and labor costs are extremely low. If to be mounted on wood, the magnet structure may be made without any mounting lugs as 37, 38, because the use of a wood screw in place of 35, may be used to hold the assembly of magnetic block 23 and its channel 34 mounted, and also serve for connecting a conductor thereto for connection in the circuit. Any suitable post element may be used to anchor the end of the trap wire 74 at 75 in FIG. 21. The venetian blind tapes in FIG. 20, serving as the trap wire, needs no spacial mounting means, for its ends are anchored to the base rail 65 and the head rail 65 respectively.

This invention is capable of numerous forms and various applications without departing from the essential features herein disclosed. It is therefore intended and desired that the embodiments shown herein shall be deemed merely illustrative and not restrictive, and that the patent shall cover all patentable novelty herein set forth; reference being had to the following claims rather than to the specific description and showing herein, to indicate the scope of this invention.

1 claim:

1. In an electrical burglar alarm system which protective circuit is normally closed and including a trap switch device in closed condition, which switch upon being opened causes the alarm circuit of the system to be actuated, such trap switch being of a type including an elongated pliable member held substantially taut by and between two support means from at least one of which support means said member is readily releasable and is caused to be released upon displacement of said member, said member being associated with a predetermined movable structure part which when moved will cause said member to be removed from said release-affording support means, the improvement comprising: said release-affording support means constituting a permanent magnetic structure consisting of a block which is a permanent magnet and a channeled sheet structure of magnetizable metal defining a channel shaped to house said block, means to hold said block tachable by and channel structure in assembly, said magnetic block being placed in said channel with at least one magnetic pole end of said magnet extending outwardly from said channel, and a conductive armature of a magnetizable composition having a surface shaped to substantially flushly fit against said one outwardly extending magnetic-pole end of said block and atmagnetic attraction alon said surface, magnetic attraction etween substantially flus surfaces of said armature and said at least one outwardly extending magnetic pole of said magnet being substantially the sole means holding said member in association with said release-affording support means, and said magnetic block being anchored in said channel, said at least one magnetic pole end of said magnet being at least partially overlappable along flush surfaces of said armature and said magnetic pole end receivable of said armature.

2. Apparatus as defined in claim 1, wherein one outwardly extending side wall of said channel-defining structure is shaped to be substantially flushly contactable with said armature surface when said armature surface is in substantially flush contact with said at least one magnetic pole end of said magnet.

3. Apparatus as defined in claim 2, wherein an opposite side of said channel extends outwardly beyond said block's said at least one magnetic pole end and an inwardly facing surface of said opposite channel side wall is shaped to substantially flushly receive a terminal end of said conductive armature when said armature is extended totally across said block with said armatures surface flush with the other outwardly extending channel wall.

4. Apparatus as defined in claim 1, wherein said magnet surface is only partially overlapped by the armature while the pliable member is in taut condition.

5. Apparatus as defined in claim 1, wherein the direction of the pliable member while in taut condition, is in any predetermined releation with respect to said surface of the magnet contacting the armature.

6. Apparatus as defined in claim 1, wherein said magnet is provided with mounting lugs extending therefrom in different planes, one of which is parallel to said magnet surface.

7. Apparatus as defined in claim 1, wherein each of the two supports of the elongated pliable member constitutes a permanent magnet structure; said member having a conductive armature at each end thereof respectively. I

8. Apparatus as defined in claim 1, wherein the block is slightly recessed in its channel.

9. Apparatus as defined in claim 1, wherein one of the side walls of the channel is provided with a mounting lug coplanar with said wall at each end of the channel, forming a notch between said lugs, whereby the armature can be set into said notch, in contact with the distal longitudinal edges of both side walls of the channel.

10. Apparatus as defined in claim 1, wherein the supports of the elongated pliable member constitute the terminals of the trap switch, and said member is conductive.

11. Apparatus as defined in claim 1, including a second permanent magnet structure positioned spaced from the first one; the annature contacting surfaces of both said magnets; said magnets constituting the terminals of the trap switch.

12. Apparatus as defined in claim 11, wherein the movable structure is a hung venetian blind which includes a base rail, a head rail and slat-supporting ladder tapes spanning and mounted on and between said rails; said tapes constituting the elongated pliable member, and the base rail being of conductive magnetizable material, serving as the armature; the permanent magnets contacting the base rail, and serving as the terminals of the trap switch. 

1. In an electrical burglar alarm system which protective circuit is normally closed and including a trap switch device in closed condition, which switch upon being opened causes the alarm circuit of the system to be actuated, such trap switch being of a type including an elongated pliable member held substantially taut by and between two support means from at least one of which support means said member is readily releasable and is caused to be released upon displacement of said member, said member being associated with a predetermined movable structure part which when moved will cause said member to be removed from said releaseaffording support means, the improvement comprising: said release-affording support means constituting a permanent magnetic structure consisting of a block which is a permanent magnet and a channeled sheet structure of magnetizable metal defining a channel shaped to house said block, means to hold said block and channel structure in assembly, said magnetic block being placed in said channel with at least one magnetic pole end of said magnet extending outwardly from said channel, and a conductive armature of a magnetizable composition having a surface shaped to substantially flushly fit against said one outwardly extending magnetic-pole end of said block and attachable by magnetic attraction along said surface, magnetic attraction between substantially flush surfaces of said armature and said at least one outwardly extending magnetic pole of said magnet being substantially the sole means holding said member in association with said release-affording support means, and said magnetic block being anchored in said channel, said at least one magnetic pole end of said magnet being at least partially overlappable along flush surfaces of said armature and said magnetic pole end receivable of said armature.
 2. Apparatus as defined in claim 1, wherein one outwardly extending side wall of said channel-defining structure is shaped to be substantially flushly contactable with said armature surface when said armature surface is in substantially flush contact with said at least one magnetic pole end of said magnet.
 3. Apparatus as defined in claim 2, wherein an opposite side of said channel extends outwardly beyond said block''s said at least one magNetic pole end and an inwardly facing surface of said opposite channel side wall is shaped to substantially flushly receive a terminal end of said conductive armature when said armature is extended totally across said block with said armature'' s surface flush with the other outwardly extending channel wall.
 4. Apparatus as defined in claim 1, wherein said magnet surface is only partially overlapped by the armature while the pliable member is in taut condition.
 5. Apparatus as defined in claim 1, wherein the direction of the pliable member while in taut condition, is in any predetermined releation with respect to said surface of the magnet contacting the armature.
 6. Apparatus as defined in claim 1, wherein said magnet is provided with mounting lugs extending therefrom in different planes, one of which is parallel to said magnet surface.
 7. Apparatus as defined in claim 1, wherein each of the two supports of the elongated pliable member constitutes a permanent magnet structure; said member having a conductive armature at each end thereof respectively.
 8. Apparatus as defined in claim 1, wherein the block is slightly recessed in its channel.
 9. Apparatus as defined in claim 1, wherein one of the side walls of the channel is provided with a mounting lug coplanar with said wall at each end of the channel, forming a notch between said lugs, whereby the armature can be set into said notch, in contact with the distal longitudinal edges of both side walls of the channel.
 10. Apparatus as defined in claim 1, wherein the supports of the elongated pliable member constitute the terminals of the trap switch, and said member is conductive.
 11. Apparatus as defined in claim 1, including a second permanent magnet structure positioned spaced from the first one; the armature contacting surfaces of both said magnets; said magnets constituting the terminals of the trap switch.
 12. Apparatus as defined in claim 11, wherein the movable structure is a hung venetian blind which includes a base rail, a head rail and slat-supporting ladder tapes spanning and mounted on and between said rails; said tapes constituting the elongated pliable member, and the base rail being of conductive magnetizable material, serving as the armature; the permanent magnets contacting the base rail, and serving as the terminals of the trap switch. 